Electron-discharge-tube amplifier system



May 14, 1929. 1.. 1.. JONES ELECTRON DISCHARGE TUBE AMPLIFIER SYSTEM Filed July 9, 1925 2 Sheets-Sheet INVENTOR. Lesfer L.Jones ATTORNEYS May.1 4, 1929. .L. LQJONES I 3 ELECTRON DISCHARGE TUBE AMBLIFIER SYSTEM Filed July 9, 1925 2 Shets-Sheet. ,2

I ATTORNEYS Patented May 14, I

: UNITED STATES LESTER L. JONES, 0F oannELf, NEW JERSEY.-

ElLECTRON-DISGH-ARGE-TUBE AMPLIFIER SYSTEM.

Application filed July 9,

' This invention relates to three-electrode vacuum tube amplifying systems, and more particularly to tuned radio frequency amplifying systems embodying electron discharge devices or tubes; and has special reference to the provision of improved means for controlling the stabilization and the energy output or volume of such tuned radio frequency amplifying systems.

The principal object of my present invention comprehends the provision of a method of and means forcontrolling the energy output or volume of electron discharge tube amplifying systems, and for simultaneously controlling the'feed-back reactions in and selectivity of the system, the present invention consisting in improvements in the method of and means/for controlling energy feedback in electron discharge devices, described and claimed in my copending application Ser. No. 743,342, filed Oct. 8,1924.

It is well known that due to the unshieldable capacity between theelectrodes, and notably between the plate and grid, of an electron discharge tube, a retransfer or feed back of energy takes place from the output or plate circuit of 'the tube to -the input or grid circuit, which energy or power feedback is highly objectionable, especially in relay, amplifying or modulating circuits, because it gives rise to distortion of the input voltage power wave form and to incipient or sustained oscillations in the grid circuit, which oscillations interfere with eflicient reception, amplification and detection of the received signals. Where a plurality of electron discharge tubes are employed in cascade, as for example in multi-stage radio frequency amplifying systems, this objectionable retransfer o1; feed-back of energy takes place through a number of channels dueto the coupling between the cascaded circuits, which maybe described as adjacent and distant stage. feedback,'the ad- F jacent stage feed-back being that moving from the plate'circuit of a tube to the grid circuit of such tube, and the distant stage feed-back being that moving from agrid or plate circuit of one tube back to the grid circuit of a preced ng tube. To produce an efficient amplifying system wherein the maximum amplification by relay action of the tube is to be obtained and wherein stability of the circuits,-ease of tuning thereof and efiicient tone quality are to be effected,

1925. Serial No. 42,399.

which consists in producing a transfer or feed-forward of energy from th grid circuit to thejplzttecircuit for prede rminedly controlling the feed-back taking place"'frgpi the pll'ate circuit to the grid circuit, this mg accomplished by the provision of 'resistance means in the plate circuit which functlons" toabstract energy from the grid ci 'cuit in ,proportion to. and corresponding li variation with the e ergy retransfer takin place from the pl te to the grid circuit across the grid-plate capacity. The present invention has forits principal object inlprovements in this method of controlling or neutralizing feed-back reactions in' amplifier circuits, and one in which the energy, output or volume of the system as a Whole may be controlled by the means for controlling the feed-back and stabilization of the system.

Further prime objects of the present invention include the provision of tuned radio frequency amplifying systems in which the amplitude of the output energy may be controlled over a Wide range of variation, as for example from one to ten thousand, without altering the filament current of the amplifier tubes; the further provision of tuned radio frequency systems in which a single control element may be employed for simultaneously controlling the amplification and the stabilization of the system; and the still further provision of improvements in tuned radio frequency amplifying systems in which the damping or selectivity of cascaded citcuits mav be predeterminedly controlled in a simple way along With the control of the energy output or amplification of the system. To the accomplishment of the foregoing and such other objects as will'hereinafter appear, my invention consists in the elements and their relation one to the other, as hereinafter particularly described and sought to be defined in the claims; reference being had to the accqmpanying drawings which show the preferred embodiments of my invention, in which: i

Fig. his a wiring diagrammatic View of a radio receiving system of the tuned radio freguency type employing two stages of radio frequency amplification and showing the principles of my present invention applied thereto,

Fig. 2 is a wiring diagrammatic View of a modification of the invention,

Fig. 3 is a graphical view exemplifying the principles of the invention, and

Fig. at is a graphical view showing the principles of the invention embodied in a modification of the control means.

Referring now more in detail to the drawings, and having particular reference first to Fig. 1 thereof, I show a radio receiving system of the tuned radio frequency type having two stages of radio frequency amplification followed by a stage of detection. This system comprises a plurality of electron discharge devices a, a and a each including a cathode or filament 10, a grid or screen 11, and an anode orplate 12, the three electrodes being contained in an evacuated envelope 13. The electron discharge device a is provided with an input or grid circuit generally designated as 11 connected to an energy receiving circuit such as the antenna circuit a, and is provided with an output or plate circuit generally designated as 0 which is linked by means of an inductive coupling device such as the transformer T to an input or grid circuit 11' associated with the electron discharge device a. The

electron discharge device w is also provided with an output or plate circuit 0" which is linked by the coupling means or transformer T to an.input circuit it of the detecting electrondischarge device or tube 0 the tube a being provided with the output circuit which may be the phone circuit 0 The first input circuit 6 may comprise the conventional tuning means such as thevario coupler T having its primary p in the antenna circuit a and its secondary s in the first grid circuit "4', and a variable tuning condenser 15 in shunt witlrthe variometer secondary a, one side of the tuning means being'connected to the grid 11 by means of the conductors 16 and 17 and the'other side of the tuning condenser being connected to the filament 10 by means of the conductors l8 and 19 and a fixed resistance 20. For heating the filament 10 to incandession, there is provided the filament circuit generally designated as f, which comprises the battery A, the negative terminal of which is connected to the filament by means of the conductors 21 and 22 and the resistance 20, and the positive terminal of which is connected to the filament by means of the conductors '23 and 24. The output circuit 0 includes the battery B, the negative terminal of which may be connected to the negative terminal of the A battery by means of the conductor 25, and the positive terminal of which is connected by means of the conductors 26 and 27 to the primary p of the coupling transformer T having the seec ondary 8 the said transformer primary beplication, which comprises a high resistance R arranged in the plate circuit 0' and so re lated to the output impedance of the transformer T and the filament plate impedance of'the tube a as to produce an abstracting or feed-forward of energy from the input circuit 2' at substantiallyv the same rate as energy is fed back from the plate circuit 0 to the grid circuit a through the grid-plate capacity of the tube, the resistance being thus effective for neutralizing the objectionable feed-back reaction taking place.

This resistance It is preferably inductancefree so that all of the available inductance may be conserved for the energy transfer from the tube a to a succeeding tube, and is preferably capacity-free, so that the resistance may be kept as small as possible to minimize the decrease of plate voltage due to the voltage drop in the plate circuit, and

so that a balance for all frequencies may be.

had. The magnitude of this resistance-is preferably from 500 to 4,000 ohms, and is generally made equal to the ratio of the filament-plate impedance to the amplification constant of the tube. The resistance should be high enough to effect the desired control,

energy from the grid circuit in proportion cence, to effect the electron discharge II1lS' to and corresponding in variation with the energy retransfer or feed-back that takes place from the plate circuit to the grid circuit. Viewed from the standpoint of the resistance relations of the interlinked circuits, the resistance R in the plate circuit has the effect of introducing a positive resistance in the grid or input circuit 6 which maybe made to neutralize the negative resistance of the grid circuit resulting from the feed-back of energy thereto. The abstraction of energy or the energy feed-forward from the input circuit produced by the resistance in the plate circuit is 90 out of phase with the energy feed-back, but takes place in each cycle so that the energy feed-back is efl'ectively compensated for or neutralized.

The eliect of the inserted resistance in the plate circuit of producing a feed-forward of energy from the input circuit'to the output circuit in opposition to the energy feed-back from the output to the input circuit may be explained on the theory that the feed-forward capacity current through the gridplate capacity is in effect magnified'by the resistance in the plate circuit due to the said resistance producing a larger than the normal voltage on the plate which is in phase with the grid voltage, and this current is in series with the inserted plateresistance, and therefore tends to abstract energy'from the preceding inputrcircuit. Thus the resistance in producing a larger inphase voltage com ponent has the effect of producing a larger capacity current, and more particularly a larger feed-forward capacity current moving from the grid to the plate; and this feed-forwardi of energy may be controlled by the size or magnitude of the resistance to nullify any' aart or the whole of the energy feed-back. This theory further explains the reason why the feed-forward of energy always equahzes the feed-back of energy independent of any change in the tube characteristics or constants, this being an important advantage flowing from the invention, such equalization of the feed-fo rward of energ with the feed-back of energy being due to t e location of the resistance inthe electronic current path. Thus with the resistance located in the output circuit, an

increase in the filament current which as known produces an increase in the feed-back of energy from the output to the input cir cuit due to an increase of the plate potential or the electronic-flow of current in the output circuit, produces a corresponding increase in the potential drop across the output resistance R, and hence a corresponding increase in the plate voltage which is in phase with the grid voltage, resulting in an increase of abstraction or feed-forward of energy corresponding with the feed-back increase. Likewise the fCMl-fUHVEILjLaIId feedback of energy will be equalized independent of any variation of the plate potential or a change in the amplication constant of the tube or any changes in the grid-plate capacity of the tube resulting from replacement or substitution of tubes of different types.

As heretofore mentioned, theprime ob-' ject of the present invention relates to im provements in this method of controlling or neutralizing feed-back reactions in amplifier systems by producing a compensating feedployed for controlling the output volume v.

of the system and the stabilizing of the circuits,, making suchcontrol of stabilization furthermore substantially independent of the tube characteristics or constants. These objectsof the invention are accomplished by the provision of potentiometer means in the plate circuit of the tube, associated with the means for coupling the output circuit to a subsequent circuit so that adj ustment of the potentiometer simultaneously controls the output energy in the output cir cuit and the stabilizationo'f the system.

Referring now to Fig. 1 of the drawings,

the invention isshown applied to the second radio frequency stage, the output circuit 0 being provided with the primary 7) "of thetransformer T, the said primary being inductively coupled to the transformer secondary s of-the next input circuit 6*, and

u QQSSOCltI-tGdAVltll the transformer prnnary p" I provide the potentiometer generally designated as P, which preferably comprises a resistance element 28 arranged across and preferably 1n shunt with the transformer primary p and a movable conta't t element 29 connected to the positive terminal of the B battery by means of the conductors 30 and 31, the plate 12 of thetube a being connected to the potentiometer-primary combination by means of the conductor 32.

As will be described more in detail hereinafter, movement of the contact 29 alongthe potentiometer resistance 28 has the efiect of controlling the feed-back and feed-tor ward reactions and the selectivity of the amplifier system as a whole and of control-. ling the energy transmitted from the output circuit 0 to the succeeding circuits, which in the embollimentof the invention exemplicircuit of the detecting tube'zfi.

Since the volume vor energy output of the system is controlledby means of the poten- 115 lied in F ig. 1 of the drawings is the input controlling rheostats, not only is the number of control units in a receiving set reduced, but the secondary effects on the tuning of the system resulting from a change of filament current are avoided. This may be seen by reference to the first radio frequency stage of the system, asshown in Fig. 1 of the drawings. If the volume or the amplitude of the output energy were'controlled by-means of varying the filament current, the input circuit 2' would be detuned due to the variation of the effective capacity of the input circuit with a change of filament current. The control of the volume or energy output by the potentiometer P inhibits the production of such detuniiig efiect s, and such volume control is therefore accomplished along with a control of stabilization of the system without the disadvantages in herent in prior systems of this character.

The detecting stage embodying the tube a may, if desired, be connected to one or more audio frequency amplifying stages, and for simplicity of illustration, the final output i vided the by-pass condensers'tl and 42.

Referring now to Fig. 2 of the drawings, I show a modification of the lnvention ap- "plied to a radio frequency system having two stzwcs of radio fre uenc am JilfiCtllZlOIl b n n and one stage of detection similar to the system shown in Fig. 1 of the drawings,

fsimilar parts being designated by similar reference characters. The system disclosed in Fig.- 2 of the drawings differs from that shown in Fig. 1 by the provision of a potentiometer control means in the output circuits and o of both radio frequency stages, the output circuit o'of both radio frequency tube a being provided with the potentiometer P, and the output circuit 0' of the second radio frequency tube a being provided with the potentiometer P a The potentiometer P is similar to that heretofore described in connection with Fig. l of the drawings, having a resistance element 28 across and preferably in shunt with the transformer primary p and having a movable contact 29 connected by means of the conductor to the positive side of the B battery, the potentiometer-primary combination being in turn connected to the plate 12 of the electron discharge device a by meansof the conductor 32. The potenti ometer 1 for the second radio frequency tubea has its movable contact connected to the plate instead of the positive terminal of the B battery, and said potentiometer comprises a resistance element 28 in shunt with the transformer primary p and a contact element, 29 connected to the plate 12 of the tube a, by means of the conductor 32, the potentiometer-transformer combination being in turn connected at its lower junction point to the positive terminal of the B battery by means of the conductor 3W. Either of the potentiometer arrangements P or P may be employed, depending upon the engineering construction of the set. In the potentiometer P the movable contact is on the high potential side of the circuit, whereas in' the potentiometer P the movable contact is on the low potential side of the alternating current circuit. Both forms of the invention may be employed with equal success, the second form being preferred when the parts of the radio receiving set are properly shielded and the first form being desirable whenthe capacity between the primary and the secondary of the transformer is maintained low.

The function of the potentiometer control and the principles of the invention may be explained by reference to Fig. 3 of the drawings, which graphically shows the volume andstabilization control produced by a plate circuit potentiometer of the type associated with the secOnd radio frequency stage a of Fig. 2 of the drawings, this potentiometer P comprising, as shown in Fig. 3 of the drawings, the resistance 28' in shunt with the transformer primary p and the movable contact 29 connected to the piste 12, the potentiometer-primary combination being .in turn connected at the lower junction point to'the 13 plus battery terminal. Preferably the resistance 28 is about ten thousand ohms, and is equal to the output impedance of the output circuit or the filament plate impedance of the tube, the output impedance of the output circuit being made equal to the filament plate tube impedance.

The energy output or volume control is effected by movement of the potentiometer contact along the potentiometer resistance, the position of the potentiometer contact determining the distribution of alternating current flowing through the primary p of the transformer. lVhen the potentiometer contact such as 29 is at the lower junction point 45 of the otentiometer-primary combination, none 0 the plate current variations traverses the primary of the transformer,

and hence the energy output is substantially zero; and as the potentiometer contact is moved from this position towards the upper junction point 46 of the potentiometer-primary combination, larger and larger fractions of the plate current variations traverse the primary coil, and this has the effect of increasing the coupling of the transformer. This increase of coupling would of itself cause an increase of theiouts put volume, were it not for the feed-back and feed-forward reactions which serve to change the receptivity of the oscillating circuits. The control of the volume or energy output of the system by this movement .of the potentiometer contact is depicted in the graph forming part of Fig.- 3 of the draw ings, by the volume curve 47, the character istic operation of the volume control being that as the. potentiometer contact is-moved from the lower junction point to theupper junction point ofthe potentiometer-trans tentiometer contact is moved from such point towards the upper junction point of the potentiometer. As will be pointed out hereinbelow, the potentiometer control may be designed to vary the configuration of the volume curve to suit the needs or requirements of service, the structure having the characteristic of great flexibility; and it will be seen from'the foregoing that the v energy output or volume of the system may a be varied over a wide ran e as for exam le from one to ten thousand, this being accomplished without altering the filament current of the amplifier tubes, the structure thus aflording a very flexible and long-range volume control.

The change of volumecontrol by the potentiometer adjustment varies the feed-back of energy from the output circuit to the input circuit, the feed-back increasing with the increasing change of volume. due to the larger alternating potentials on the plate as the effective transformer coupling is increased. This is depicted in the graph of Fig. 3 of the drawings by the curve 49 calibrated in-terms of the negative feed-back resistance of the grid circuit produced by the feed-back of energy. It will be seen that as the potentiometer contact moves fromthe lower to the upper junction point of the potentiometer, the negative feed-back resistance increases from a minimum to a maximum value.

The function and principle of operation of the potentiometer adjustment for controlling the stabilization oi'the system, that is, the suitable control of the feed-back reactions so as to eliminate the "oscillations and obtain proper tone quality and the suitable control of the damping factor'of the input circuit so as to get the right broadness of tuning or selectivity of the system, is also graphically depicted in Fig. 3 of the draw- .ings, by means of the curve 50, which is cal- .ibrated in terms of the positive feed forward resistance of the grid circuit produced by the potentiometer adjustment. By reference to Fig. 3, it will be seen that as the potentiometer contact is moved from the lower junction point to the upper junction point of the potentiometer, the feed-forward resistance, that is, the resistance which is in phase with the grid potential, increases from a value as shown by the curve 51,'which is the circuit ohmic res1stance,-to a maximum value which is reached when the potentiometer contact is Substantially at the mid-point of the potentiometer resistance, the feed-forward resistance then decreasing from such maxlmum value to that of the grid circuit ohmic resistance.

The inter-relation of the volume .and stabilization controls by means of the potentiometer may be seen from the inter-reactions of the curves 47-50, as shown in Fig. 3 of thedrawings 5 The control regions may for the. purpose of analysis be subdivided into the regions A, B, G and D. Considering first the feed-back and feed-forward curves 49 and 50, it will be seen that these intersect at a point X, the region between these curves to the left of the intersecting point corresponding to the elfective damping resistance of the gridcircuit, and hence to the broadness of tuning of the same, this being represented for example by the 0rdi-' nate 52; while the region between the curves to the right of the intersecting point X corresponds to the intensity of self-generated oscillations, the same being shown, for example, by the ordinate 53 at a given point of adjustment. As the potentiometer contact is moved dowri from the top junction point 46 of the potentiometer in the region A, the self-generated oscillations become weaker, until the intersection or crossing point X is reached, and at this point the oscillations cease, as shown by the intersection of the volume and oscillation curves 4;? and 48. I During this adjustment, it will bejseen that the positive feed-forward resistance is gradually increased until the feed-' forward resistance equals and hence neutralizes. thefee'd-back resistance, the point of neutralization corresponding to the point at which oscillations are eliminated. This region A 'is useful in the manipulation of the receiver when the' receiver app ars dead to determine whether or not the atteries and tubes are faulty. Thus if no oscillations .resultas the potentiometer is moved into the region A, clear indication is had that the absence of signal is due either to run-down batteries or defective tubes.

The region A forming part of the region of adjustment A is that between the maximum permissible selectivity and the maximum volume obtainable, and in this region the re-adjustments at maximum sensitivity for distant-stage feed-back and atmospheric variations can be carried out. In a complete receiver, some adjustment is required to prevent the antenna or first input circuit from generating self-oscillations or from becoming greatly over-damped due either to distant stage feed-back variations, or due to variations of the antenna resistance resulting from variable atmospheric conditions. Where oscillation results from distant stage feed-back, the method of cutting down the amplification of the system to stop the oscillations usually results in a considerable loss of volume. With the present system, however, by adjusting the potentiometer in the region A, the small necessary changes in the damping 'of the input circuit can be effected so as to stop the disturbing oscillations without any substantial loss of volume.

The adjustment region B corresponds to approximately constant volume, as shown by the curve 47, with a variable selectivity or damping of the circuits as shown by the ordinates between the curves 49 and 50, the selectivity or damping being variable usually in the order of from .01 to .05 (log. dec.) in receivers having three tube circuits. In this region the feed-back and feed-forward resistances substantially balance, the change in their difference being the factor which causes the variation of selectivity. This range of operation is useful for pick-up work, since the receiver is broadly tuned and yet has the desired sensitivity.

The operating region C is one of variable volume and selectivity, marking a transition into the operating region D, in which latter the receiver has constant selectivity and variable volume. The region I) is that in which the majority of reception is performed, as from stations up to fifty miles distance. In this region the receiver has a moderate selectivity corresponding substantially to the normal ohmic resistance of the circuits without any reaction components. In this region the volume is variable over an extremely wide range, namely, from zero signal on the strongest local stations up to approximately one-third of the maximum sensitivity of the receiver.

Ihe particular configuration that the volume curve assumes is dependent upon a num- :ber of factors, such as the inter-relation of the feed-back and feed-forward curves and the design of the .potentiometer resistance; and where, as shown in Fig. 3 of the drawings, the resistance is uniformly distributed in the potentiometer, to volume curve first rapidly increases with the potentiometer adjustment, and then increases more slightly until the constant value is reached, and thereafter increases again up to the point of oscillation.

Therelatively slow increase of volume in the region C is due to the oppositely working factors of increased transformer coupling and increased damping of the oscillatory circuit. The transformer coupling in this region is increasing would of itself produce a more rapid increase of volume, but this is in part negare ion of A ad'acent to re ion B further 0 D J b 7 increases of volume may be obtained, but these are normally not useful, since in this region the selectivity of the set becomes so great as to introduce distortion of the audio tone quality due to the inability of the cir- 35 cuits to transmit the whole wave band corresponding to the modulated carrier wave,

for as Wlll be understood by those skilled in the art, when the resistance of the input circuit is very large, the circuit has high damping and is broadly tuned, and when this resistance is moderate, the circuit is more selective, and when the resistance is nearly zero, the circuit is super-selective, that is, it

tunes so sharply that only part of the modulated wave band is received; and when the resistance is zero or less, the circuit tends to oscillate of its own accord.

One of the important problems. in the proper design of a stabilizing control means is to so design and construct the control instrumcntalitics that. all of the circuits will receive substantially the same changes in damping during adjustment. This is accomplished by the potentiometer system of my present invention, the damping 0r selectivity of all the circuits being changed in the same direction during the potentiometer adjustment. Thus, referring to Fig. l of the drawings, the variation of the potentiometer P serves to control the damping of the tuned circuits and '11, and this occurs because if the resistance effective for feed-forward in the potentiometer be increased, the damping of the input circuit 71 is increased, and an 1 increase of dampingcin this circuit has the effect of reducing the impedance in the output circuit 0 of the first radio frequency tube, which in turn reduces the feed-back through such tube. Since the feed-forward through the first radio frequency tube is left constant, the input circuit i has a preponderance of feed-forward or energy loss, and therefore its damping is also increased. During the potentiometer adjustment, the 1 third tuned circuit 2' sustains a corresponding increase of damping due to the fact that the plate resistance of the tube a is connected more fully in parallel with the potentiometer resistance, tending to reduce the quite rapidly, and 70 resistance across the primary coil of the transformer T the reduction of this resistance causmg the increase 1n the damping of the tuned circuit 1?. The damping of all ofthe tuned circuits therefore is changed in the same direction with the potentiometer adjustment, and therefore the selectivity of the receiver as awhole,that is, of each adjustable tuning unit, is affected in thesame direction By means of the potentiometer of my invention, therefore, one circuit will not be over-damped in comparison with another circuit during the potentiometer adjustment, and the diiferent circuits will receive substantially similar changes in the damping factor. i

- The potentiometer resistance may be designeddepending upon the operating characteristics which are desired for the receiver. Referring again to 'Fig. 3 of the drawings, the operating range D is thatof constant. selectivity with variable volume, while the operating range B is conversely that of constant volume with variable selectivity. Where it is desired to control the selectivity. without change in volume, the

resistance of the potentiometer may be distributed to produce the curve shown in Fig. 3 of the drawings. The operating region A is a critical region, and is of greater relative importance than the remainder of the operating region A, and this region A. may be made larger by suitable distribution of the potentiometer resistance. Since from a practical operating viewpoint the region D is more suitable than the. region B, the potentiometer resistance as a whole may be region A, which may be considered as the super-selectivity and oscillation-control region, may be suitably lengthened, and the remainder of the region A, which is of rela tively small utility, may be considerably decreased in range. Similarly, the region D, which is that of. constant selectivity with variable volume, and the adjoining region G having variable volume and slightly variable selectivity, may be made to occupy more than fifty per cent of the otentiometer dial range, with-the region reduced to relatively small proportions.

The use and operation of the volume and 'points of said shunt impedance.

stabilization control system of my invention and the many advantages thereof .will in the main be fully apparent from the detailed description thereof. It will be further apparent that numerous changes may be made 7 111 the arrangement and control elements of the potentiometer without departing from the spirit of the invention, defined in the following claims.

I claim;

1. A radio frequency amplifier comprising an electrondischarge .tube having a grid circuit, a plate circuit and a filament system, coupling means for coupllng the plate circult to asubsequent circuit and mechanism so for controlling the feed-back reactions between the grid andplate of said tube comprising an impedance in the plate circuit in shunt with the plate circuit component of said coupling means, the plate electrode and the filament system being connected to selected tap points fof said shunt impedance.

2. A radio frequency amplifier comprising an electron discharge tube having a grid circuit, a plate circuit anda filament system, a transformer couplingmeans for coupling the plate circuit to a subsequent circuit and-mechanism for controlling thefeed-back reactions between the grid and plate of said ca tube comprismg a resistor impedance in the plate circuit inshunt with the primary of' said transformer coupling means, the plate electrode and the filament system being connected to suitably tapped points ofsaid shunt impedance. V

3. A radio frequency amplifier comprising an electron discharge'tube having a grid circuit, a plate circuit and a filament system,

a tuned circuit, inductive coupling means for coupling the said plate circuit to the'tuned circuit and mechanism for neutralizing the feed-back reactions via the grid and plateletsaid tube due to said coupling means and tuned circuit comprising an impedance in the plate circuit in sin-int with the inductive plate circuit component of said coupling .means, the plate electrode and the filament system being connected to selected tapped 4..A radio. frequency amplifier system comprising an electron discharge tube having a grid circuit, a plate circuit and a filament system, inductive coupling means for coupling said plate circuit to a subsequent 12 circuit, and mechanism for simultaneously fixing the degree of coupling of said coupling means and the feed-back reaction across the grid and plate electrodes, said mechanism comprising an impedance in the said platen- 5 circuit in shunt with the plate circuit component of said coupling means, and connections'betwcen said plate electrode and filament system with tapped points on said shunt impedance. v

5. A radio frequency amplifier system comprising an electron discharge tube having a grid circuit, a plate circuit and a fila- 'IHBllt system, a tuned circuit, transformer coupling means for coupling said plate circuit to said tuned circuit, and mechanism for simultaneously fixing the degree of coupling of said" coupling means and the feed-back reaction across the grid and plate electrodes, said mechanism comprising a resis-tor impedance in the said plate circuit in shuntwith the primary of said transformer coupling means, and connections between said plate electrode and filament sys-. tem with selected tapped points on said shunt impedance.

(5. A radio frequency amplifier system comprising an electron discharge tube having a grid circuit, a plate circuit and a filament system, coupling means for coupling said plate circuit to a subsequent circuit, and nieclianisnifor simultaneously fixing the degree of coupling of said coupling means and the feed-back reaction acrossthe grid and plate'clectrodes, said mechanism comprising 'an impedance in the said plate circuit in shuntwith the plate circuit component of said coupling means, and connections between said plate electrode and filament system with selected points on said shunt impedance, the coupling means and said impedance having constants for producing an effective feed-forward resistance in said plate circuit balancing the feed-back resistance component which is due to the inductive, reactance of said coupled circuits.

7 A radio frequency amplifier system comprising an electron discharge tube having a grid circuit, a plate circuit and a filament system, a tuned circuit, transformer coupling means for-coupling saidplate circuit to said tuned circuit, and mechanism for simnltaneously fixing the degree of coupling of said coupling feed-back reaction across the grid and plate electrodes, said mechanism comprising a resistor impedance in the said plate circuit in shunt with the primary of said transformer coupling means, and connections between said plate electrode and filament system with suitable points on said shunt impedance, the

transformer coupling means and said impedance having constants for producing an effective feed-forward resistance in said means and the.

means to form therewith a shunt circuit having two branches, and connections from the plate and filament of the tube to said shunt circuit, said' connections being made to points in the shunt circuit so that components of both theconpling means and impedance are included in at least one branch of said shunt circuit.

-9. A radio frequency amplifier comprising an electron discharge tube having a filament, a grid and a plate, a tuned circuit, a plate circuit including a coupling means for coupling said plate circuit to the tuned circuit, and mechanism for controlling the feed-back reactions between the grid and plate of said tube comprising an impedance connected across said coupling means to form therewitha shunt circuit having two branches, and connections from' the plate and filament of the tube to said shunt circuit,

said connections being made to points in the shunt circuit so that components of both the coupling means and impedance are included in at least one branch of said shunt circuit.

10. A radio frequency amplifier comprisingan electron discharge tube having a grid circuit, a plate circuit and a filament system, a coupling transformer having its primary in the plate circuit and having a tuned secondary, and means for controlling the feed-back .reactions between 'the grid and plate of said tube comprising a potentiometer inthe said plate circuit in shunt with said transformer primary and connections between the plate and filament of the tube with said potentiometer, said connections being adjustable to simultaneously vary the in series resistance of the plate circuit and the alternating current potential across the transformer primary.

11. An amplifying system comprising a three electrode tube embodying a filament, a

grid and a plate, a grid circuit, a plate circuit,a coupling transformer having its primary in the plate circuit, and a high resistance potentiometer connected across said transformer primary, the potentiometer resistaiice being of the order of magnitude of the filainent plate-impedance of the tube.

12. An amplifying system comprising a three electrode tube embodying a filament, a grid and a plate, a grid circuit, a plate circuit, a coupling transformer having its pri mary in the plate circuit, and a high resistance potentiometer connected across said transformer primary, the potentiometer resistance being substantially equal to the filas ment-plate-inipedanee of the tube, the same being equal to the output impedance of the plate circuit.

Signed at New York city, in the county of New York and State of New York, this 6th day of July, A. D. 1925.

LESTER L. JONES. 

